Effects of Acute Hypoxic Stress on Physiological and Hepatic Metabolic Responses of Triploid Rainbow Trout (Oncorhynchus mykiss)

Abstract

This experiment simulated the hypoxic environment caused by actual production operations in fish farming (i.e., catching, gathering, transferring, and weighting) to study the effects of acute hypoxic conditions on the physiological and metabolic responses of triploid rainbow trout (O. mykiss). Two groups of fish weighting 590 g were sampled in the normoxia group (dissolved oxygen above 7 mg/L) and hypoxia group (dissolved oxygen ranged from 2 to 5 mg/L for 10 min). The results showed that 1) regarding stress response, hypoxia increased plasma levels of cortisol, heat shock protein 70 (HSP-70), lysozyme, alanine aminotransferase (ALT), aspartate aminotransferase (AST) and creatine phosphokinase (CPK); induced the expression of hepatic genes encoding nuclear factor erythroid 2 related factor 2 (Nrf2), interferon γ (IFN-γ) and interleukin-1β (IL-1β). 2) Regarding metabolism response, hypoxia increased plasma levels of globulin (GLOB), glucose (GLU), triglyceride (TG) and lactate dehydrogenase (LDH); upregulated the hepatic gene expression of phosphoenolpyruvate carboxykinase, (PEPCK), pyruvate dehydrogenase kinase (PDK1), acetyl-CoA carboxylase (ACC) and acetyl-CoA oxidase (ACO); downregulated the hepatic gene expression of carnitine palmitoyl transferase 1 (CPT1); and unchanged the expression of hepatic genes in glycolysis and autophagy. 3) In response to hypoxia-inducible factors (HIFs), the hepatic HIF-2α gene was activated in the hypoxia group, but HIF-1α gene expression remained unchanged. Thus, during acute hypoxic stress, triploid rainbow trout were in a defensive state, with an enhanced immune response and altered antioxidant status. Additionally, the hepatic mitochondrial oxidation of glucose- and lipid-derived carbon in trout was suppressed, and hepatic gluconeogenesis and lipid synthesis were activated, which might be regulated by the HIF-2α pathway.

Keywords: HIF-2α; acute hypoxia; metabolism; physiology; triploid rainbow trout.

FIGURE 1

Effect of acute hypoxic stress on the expression of the hypoxia-related genes in the liver of triploid rainbow trout (n = 6; HIF-1α, hypoxia-inducible factor 1α; HIF-2α, hypoxia-inducible factor 2α; FIH1, factor inhibiting hypoxia-inducible factor 1; PHD2, egl nine 1-like protein). Asterisks indicate the significant difference (t-test; *p < 0.05; **p < 0.01).

FIGURE 2

Effect of acute hypoxic stress on the malondialdehyde (MDA) content in the plasma (A) and liver (B) as well as the total antioxidant capacity (T-AOC) level in the plasma (C) and liver (D) of triploid rainbow trout (n = 6). Asterisks indicate the significant differences (t-test; *p < 0.05; **p < 0.01).

FIGURE 3

Effect of acute hypoxic stress on the expression of the antioxidant-related genes in the liver of triploid rainbow trout (n = 6; Nrf2, nuclear factor erythroid 2 related factor 2; SOD, superoxide dismutase; CAT, catalase; GPx, glutathione peroxidase). Asterisks indicate significant differences (t-test; *p < 0.05; **p < 0.01).

FIGURE 4

Effect of acute hypoxic stress on the expression of the immune-related genes in the liver of triploid rainbow trout (n = 6; IFN-γ, interferon γ; TNF-α, tumor necrosis factor-α; HSP-70, heat shock protein 70; IL-1β, interleukin-1β; IL-8, interleukin-8). Asterisks indicate significant differences (t-test; *p < 0.05; **p < 0.01).

FIGURE 5

Effect of acute hypoxic stress on the expression of the glycometabolic genes in the liver of triploid rainbow trout (n = 6; GLUT2, Glucose transporter 2; GYPL, Glycogen phosphorylase liver form-like; GK, Glucokinase; PDK1, Pyruvate dehydrogenase kinase; LDHA, L-lactate dehydrogenase; PEPCK, Phosphoenolpyruvate carboxykinase; G6Pase, Glucose-6-phosphatase; GYS, Glycogen synthase). Asterisks indicate significant differences (t-test; *p < 0.05, **p < 0.01).

FIGURE 6

Effect of acute hypoxic stress on the expression of the lipometabolic genes in the liver of triploid rainbow trout (n = 6; CPT1, carnitine palmitoyl transferase 1; ACO, acetyl-CoA oxidase; ACC, acetyl-CoA carboxylase; FAS, fatty acid synthase; ADRP, adipose differentiation-related protein). Asterisks indicate significant differences (t-test; *p < 0.05, **p < 0.01).

FIGURE 7

Effect of acute hypoxic stress on the expression of the autophagy-related genes in the liver of triploid rainbow trout (n = 6; LC3β, microtubule associated protein 1 light chain 3 beta; gabarapL1, gamma aminobutyric acid receptor-associated protein; atg4b, autophagy-related 4β; atg12L, autophagy-related 12L). Asterisks indicate significant differences (t-test; *p < 0.05; **p < 0.01).